(1) Field of the Invention
The present invention relates to broadcast receiving circuits and broadcast receiving apparatuses and, in particular, to a broadcast receiving circuit and a broadcast receiving apparatus capable of switching among services received in digital broadcasting for viewing the services.
(2) Description of the Related Art
The Japanese terrestrial digital TV broadcasting system has each frequency band for one channel divided into 13 segments. For stable reception of programs on mobile receivers, such as cellular phones, one of the 13 segments is left for the mobile receivers. This is called the One-Segment broadcasting service (hereinafter referred to as One-Seg broadcasting). Other than the one segment for the One-Seg broadcasting, the rest of the 12 segments are used to provide a service (hereinafter referred to as the 12-Seg broadcasting) for receiving a high-definition television (HDTV) broadcast with a stationary TV. The 12-Seg broadcasting is not as capable as the One-Seg broadcasting in terms of stable reception. The 12-Seg broadcasting and the One-Seg broadcasting, each of which employs a different kind of coding technique, usually provide the same program at the same time. Such broadcasting is referred to as the simulcast.
Some on-vehicle digital broadcast receiving apparatuses receive digital broadcasts, taking advantage of the feature of the simulcast. The on-vehicle digital broadcast receiving apparatuses use a technique to switch between the 12-Seg broadcasting and the One-Seg broadcasting, and provide the selected broadcasting on a display apparatus, such as a monitor, depending on a reception condition of the digital broadcasting. This technique allows the program to be continuously provided to the viewers regardless of the reception condition of the digital broadcasting.
In Japan, however, the simulcast is not mandatory in operating a broadcast station. Thus the 12-Seg broadcasting and the One-Seg broadcasting could provide different programs at the same time. Hence when a viewer unconditionally switches from the 12-Seg broadcasting to the One-Seg broadcasting on the assumption that the broadcastings are simulcast, the program which the viewer is watching might be switched to another program that the viewer is not expecting. This makes the viewer feel uncomfortable.
Taking such a problem into consideration, a proposed broadcast receiving apparatus determines whether or not the simulcast is provided on the same channel, and, in the case where the apparatus determines that the simulcast is provided, the proposed broadcast receiving apparatus switches between the 12-Seg broadcasting and the One-Seg broadcasting to provide the selected broadcasting (See Patent Reference 1: Japanese Unexamined Patent Application Publication No. 2007-295468).
In order to detect whether or not the program is simulcast, the Patent Reference 1 compares a soundless period of audio data included in the 12-Seg broadcasting with that of audio data included in the One-Seg broadcasting. The Patent Reference 1 assumes the case where a soundless state continues as long as a predetermined time period or longer. Specifically, assumed is the case where a Transmission and Multiplexing Configuration Control (TMCC) signal, which is included in a broadcast wave in advance, has control information transferred thereto. Here the control information indicates whether or not the program is simulcast. Then, at a receiver, assumed is a case where (i) the control information is referred to, and (ii) a decode error has developed due to bad reception in both of the 12-Seg broadcasting and the One-Seg broadcasting.